Need better interface to rename / merge tags

[razzius]

Currently in the admin, you can only delete tags if there are no associated profiles.

Workaround: edit a profile as admin, update the tag to the preferred one, which removes the profile-tag association, then delete the old tag in the backend.

A better interface would be to select a tag in the admin, view the profiles it is attached to, enter a new tag for it to merge into, then update the profile-tag relations and delete the tag in the database.

[jjchen20]

Related to #186:

• On the admin back end, create way to merges similar tags, i.e. mentoring and mentorship
• Identify what to merge (i.e. Mentoring, Mentorship) --> Describe what to merge to (i.e. Mentoring)